Medical amplifier isolation

ABSTRACT

This disclosure provides isolation for a medical amplifier by providing a low impedance path for noise across an isolation barrier. The low impedance path can include a capacitive coupling between a patient ground, which is isolated from control circuitry, and a functional ground of an isolation system that is isolated from earth ground. The low impedance path can draw noise current from an input of an amplifier of patient circuitry.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.14/434,922, filed Apr. 10, 2015 and entitled MEDICAL AMPLIFIERISOLATION, which claims priority to PCT/US2013/064595, filed Oct. 11,2013 and entitled MEDICAL AMPLIFIER ISOLATION, which claims priority toU.S. Provisional Application No. 61/713,022, filed Oct. 12, 2012 andentitled MEDICAL AMPLIFIER ISOLATION. Each of the above-identifiedapplications is incorporated herein by reference in their entirety.

TECHNICAL FIELD

This disclosure relates to medical amplifier isolation systems andmethod.

BACKGROUND

Medical amplifiers can be implemented for a variety of devices used inconnection with patient treatment procedures and/or medical diagnoses.Medical amplifiers can be configured in a manner to isolate a patientfrom any possible contact with a power source, such as including linevoltage and earth ground. Isolation can be implemented in a variety ofways, such as magnetic or optical isolation, to pass signals between acontrol system and portions of the device that might contact thepatient. Some types of isolation can result in the medical amplifierbeing more susceptible to radiated noise, such as line frequency noise,based on the patient ground not being coupled with earth ground. Inthese situations, a substantially large common-mode voltage with respectto earth ground can be generated, such that the common-mode voltagegenerates a current flow from the patient to earth ground via aparasitic capacitance, thus generating a differential voltage thatcannot be rejected by the medical amplifier.

SUMMARY

This disclosure relates to isolation for a medical amplifier system.

As an example, a medical amplifier system includes a patient circuitrystage configured to receive electric signals from the patient andprovide corresponding output signals. The patient circuitry stage caninclude an electrical connection to a patient ground. The system alsoincludes control circuitry configured to process the correspondingoutput signals. An isolation system can be configured to electricallyisolate the patient circuitry stage and the control circuitry byincluding a functional ground that is capacitively coupled to thepatient ground but electrically isolated from the control circuitry.

As another example, an apparatus can include an isolation systemconfigured to be connected between and provide electrical isolationbetween patient-side circuitry and other circuitry. The isolation systemcan include a patient isolation stage comprising at least one signalinput configured to connect to a signal path of the patient-sidecircuitry and a power input configured to connect to a power path of thepatient circuitry. At least one other isolation stage can be connectedbetween the patient isolation stage and the other circuitry. Such otherisolation stage can include a corresponding signal path configured tocommunicate signals from the signal path of the patient-side circuitrysignal to the other circuitry and a separate power path configured toprovide input power from the other circuitry to the power path of thepatient isolation stage. A capacitive coupling is connected across thepatient isolation stage between a patient ground of the patient-sidecircuitry and a functional ground of the isolation system, the otherisolation stage being configured to electrically isolate the functionalground from the other circuitry.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example of a medical amplifier system implementing anisolation system.

FIG. 2 depicts an example diagram of medical amplifier system that canbe implemented.

FIG. 3 depicts another example diagram of a medical amplifier system.

DETAILED DESCRIPTION

This disclosure relates to medical amplifier isolation systems andrelated methods. As an example, a medical amplifier system can includean isolation system that includes multiple stages of isolation betweenpatient circuitry, including an amplifier, and non-isolated control andprocessing circuitry. A capacitance can be provided across apatient-side isolation barrier, such as by capacitively coupling apatient ground and an isolated functional ground. The capacitancebetween such grounds can establish a lower impedance path for noisecurrent than parasitic capacitors to earth ground in the amplifiersystem. The medical amplifier thus can substantially reduce themagnitude of current flowing between the patient and earth ground via aparasitic capacitance, resulting in an increased signal to noise ratio,while also being capable of meeting or exceeding standard requirementsfor isolation and leakage current.

FIG. 1 depicts an example of a system 10 that includes medical amplifiersystem 12. The medical amplifier system 12 can be implemented in avariety of medical applications for administering treatment to orobtaining diagnostic information from a patient 14, for example. Themedical amplifier system 12 includes a patient circuitry stage 16 thatcan be coupled to the patient 14 via electrically conductive leadsterminating to sensor elements 18, such as electrodes or probes. Thesensor elements can be passive sensor electrodes or active circuitcomponents can also be implemented at the electrodes.

The patient circuitry stage 16 can thus receive signals SGNL_(PTNT) fromthe patient 14 via the sensor elements 18. There can be any number ofsensor elements 18, and the patient circuitry 16 can include circuitryfor processing signals provided by each such conductors. The sensorelements 18 can be non-invasive (e.g., positioned on the surface of thepatient's body) and/or be invasive (e.g., percutaneously or otherwisepositioned within the patient's body).

In the schematic example of FIG. 1, the patient circuitry stage 16includes signal circuitry 20 and power circuitry 22. The patientcircuitry 16, including the signal circuitry 20 and power circuitry 22,can operate electrically relative to a patient ground 24. The powercircuitry 22 can be configured to deliver electrical power (e.g.,regulated DC power) to the patient circuitry 16, including the signalcircuitry 20. While for purposes of ease of explanation the signalcircuitry 20 and the power circuitry 22 are demonstrated as separateblocks, it is to be understood that power and processing circuitry canbe structurally integrated together in other examples.

The signal circuitry 20 can include one or more amplifiers that can beconfigured to amplify each of the patient signals SGNL_(PTNT), such asanatomically generated electrical impulses. The signal circuitry 20 canbe configured to amplify the signals SGNL_(PTNT) and providecorresponding amplified signals SGNL_(AMP) to one or more correspondingnon-isolated circuitry 32. The non-isolated circuitry 32 can operateelectrically relative to an earth ground that is electrically isolatedfrom the patient ground 24. Specifically, the amplifier system 12includes an isolation system 25 configured to electrically isolate thepatient circuitry from the non-isolated circuitry 32.

As a further example, the signal circuitry 20 can be configured (e.g.,by including an analog-to-digital converter) to provide the amplifiedsignals SGNL_(AMP) as digital signals. As an example, the non-isolatedcircuitry 32 can include processing circuitry, such as to implementsignal conditioning and filtering on the amplified signals SGNL_(AMP)provided by the isolated patient circuitry 16. The non-isolatedcircuitry 32 can in turn provide processed version of the amplifiedsignals SGNL_(AMP) for subsequent processing (e.g., by an EC mappinghardware and software and/or other diagnostic equipment) via the signalpath.

In other examples, the non-isolated circuitry 32 can generate controlsignals to the patient circuitry stage 16 and/or the patient 14. Forexample, the control signals can be utilized to configure the patientcircuitry stage 16, including the signal circuitry 20. As anotherexample, the control signals may be used to control delivery of therapyto the patient 14 across the isolation system 25. Control signals canalso be generated by the patient circuitry 16 and provided to thenon-isolated circuitry 32 via the signal path through the isolationsystem 25.

The isolation system 25 is configured to electrically isolate thepatient circuitry 16 from the non-isolated circuitry 32. The isolationsystem 25 can include more than one isolation barrier 26 and 30. Eachisolation barrier 26, 30 can be configured to provide one type ofisolation for data/information signals (e.g., optical isolation) andanother type of electrical isolation (e.g., magnetic isolation) forpower signals that are being provided between the patient circuitry andthe non-isolated circuitry 32. Other types of isolation can beimplemented for communication of data and power between the patientcircuitry and the non-isolated circuitry.

In the example of FIG. 1, the non-isolated circuitry 32 can be coupledto receive input power from a power source (not shown—e.g.,approximately 120 VAC/60 Hz or 230 VAC/50 Hz or regulated DC power). Forinstance, the non-isolated circuitry 32 can be connected between a linevoltage and earth ground 36. The isolation system 25 thus is configuredto provide electrical isolation between the patient 14 and the powersource, such that a patient ground 24 is not electrically coupled withearth ground 36 to which the circuitry 32 is connected. The data andinformation signals (e.g., including the signals SGNL_(AMP)) and powercan thus be communicated across the isolation system 25 between thenon-isolated circuitry 32 and the patient circuitry 16. In the exampleof FIG. 1, while the non-isolated circuitry 32 is demonstrated ascoupled to earth ground 36, it is to be understood that the low-voltagerail reference could be a variety of low-voltage amplitudes electricallyisolated from patient ground 24, and is not limited to earth ground.

In some circumstances, the isolation system 25 can render the medicalamplifier system 12 more susceptible to radiated noise, such as linefrequency noise or other noise that exists within the bandwidth beingmeasured. This susceptibility is based on the isolation of the patientground 24 with respect to earth ground 36. Isolating the patient 14 canresult in the patient ground voltage potential to “float”, such as basedon electric fields acting upon the patient 14, and thus inducing aleakage current to flow from the patient ground 24 to earth ground 36via a parasitic capacitance C_(P). The parasitic capacitance C_(P) isdistributed around the device and the cabling, so currents through anypart of the device will vary. As a result, the patient circuitry stage16 can generate a substantially large common-mode voltage with respectto earth ground 36. The common-mode voltage can generate a common-modecurrent that can induce a differential voltage in the amplified signalsSGNL_(AMP) that cannot be rejected by the medical amplifier system 12.For example, the common-mode current flow can instantiate a differentialvoltage with respect to input resistors associated with the signalcircuitry 20, which can be transmitted as noise in the signalsSGNL_(AMP). The amount of current flow leakage may be reduced byemploying matched resistors, but this alone still tends to beinsufficient for achieving high common mode rejection (e.g., greaterthan −100 dB, such as about −140 dB or more).

To substantially mitigate the common-mode current flow, the medicalamplifier system 12 includes a capacitive coupling C_(GND) connectedacross the patient isolation system 25 between the patient ground 24 anda functional ground 28 residing between separate isolation stages in theisolation system. For example, the capacitive coupling C_(GND) can beconfigured as one or more physical capacitors having a capacitance thatis greater than the parasitic capacitance C_(P). As a result, thecapacitive coupling C_(GND) can provide a lower impedance path acrossthe isolation system 25. The low impedance path effectively causes thefunctional isolation stage to float at approximately the same voltage asthe patient isolation stage. Such a low-impedance path substantiallyreduces a voltage difference across the parasitic capacitance C_(P). Asa result, a substantially large portion of the leakage current that cancause the common-mode current can flow through the capacitive couplingC_(GND) instead of the parasitic capacitance C_(P), resulting insignificantly reduced leakage current and correspondingly reduceddifferential voltage at the input of the signal circuitry 20. As afurther result, the sensed signals at the input of the amplifier exhibitan improved common mode rejection ratio (e.g., by about 20 dB or more).

Additionally, the total amount of leakage current in the system 10 isabout the same as a system having a single isolation barrier. This isbecause the magnitude of the leakage current is determined by the sizeof the parasitic capacitors at the patient stage, and across the finalisolation barrier to earth ground. Since the size of the parasiticcapacitors does not change when a functional isolation stage is added,such as disclosed herein, patient safety is not compromised.

FIG. 2 depicts a schematic diagram of an example of a medical amplifiersystem 50 that can be implemented. The amplifier system 50 includes apatient-side circuitry stage 52, such as can correspond to the patientcircuitry stage 16 of the medical amplifier system 12 in the example ofFIG. 1. Therefore, reference can be made to FIG. 1 in the followingdescription of the example of FIG. 2.

The patient circuitry stage 52 includes an amplifier 54 that isconfigured to generate an amplified signal SGNL_(AMP) in response to apatient input signals SGNL_(PTNT). The patient signals SGNL_(PTNT) cancorrespond to one or more electrical signals measured from the patient,such as via conductive elements (e.g., sensor electrodes) that arecoupled to the patient. In some examples, the conductive elements can beelectrodes distributed across a patient's torso, such as non-invasivelycovering the entire torso or a predetermined portion thereof. Forinstance, the electrodes can be arranged on the patient's torso, such asfor acquiring electrical signals for electrocardiographic mapping or forgathering electrocardiograph (ECG) or electroencephalograph (EEG)diagnostics. Additionally, each electrode can define a respective inputchannel that provides a corresponding patient signal SGNL_(PTNT) to arespective amplifier 54, each of which amplifiers can be electricallyisolated based on the teachings herein. The amplifier 54 as well asother patient-side circuitry 52 can be powered by patient-side powercircuitry 62 that is supplied power via a power path of an isolationsystem 63 such as disclosed herein. The power circuitry 62 thus canestablish a high voltage rail (e.g., a regulated voltage) demonstratedas V+ that is relative to a low voltage rail corresponding to patientground 60. The power circuitry 62 can similarly also, for example,establish a negative voltage rail V− (not shown) relative to the patientground 60.

In the simplified example of FIG. 2, the amplifier 54 can include afirst input resistor R₁ coupled to a non-inverting input and a secondinput resistor R₂ coupled to an inverting input. The amplifier 54 thusprovides an amplified output signal SGNL_(AMP) to signal processing andcontrol circuitry (not shown, but see, e.g., circuitry 32 of FIG. 1)through two or more isolation stages, demonstrated at 64 and 66. Eachisolation stage 64, 66 can be configured to communicate power and datain a manner that affords electrical isolation between the input andoutput thereof. Since the manner of electrical isolation beingimplemented can vary according to design considerations and applicationrequirements, the isolation for data and power are demonstrated asdotted lines extending across the blocks corresponding to the isolationbarriers 64 and 66. As mentioned above, for example, optical isolationcan be utilized for communicating data, such as by employing digitaloptical communication of the amplified output signal SGNL_(AMP).Magnetic or inductive electrical isolation (e.g., via a transformer) canbe employed to communicate the power across each isolation barrier 64and 66, for example.

In the example of FIG. 2, the medical amplifier system 50 isdemonstrated as including a voltage source 58 to represent a noisevoltage V_(NOISE) that can be applied onto the patient signalsSGNL_(PTNT). In the absence of an isolation system implemented based onthe teachings herein, the voltage V_(NOISE) induces a current to flowthrough each of the input resistors R₁ and R₂, demonstrated in theexample of FIG. 2 as currents I₁ and I₂, respectively. These currentswill vary since the parasitic capacitance differs across the differentparts of the circuits. The magnitudes of the induced currents I₁ and I₂can also vary relative to each other based on variations in the internalcomponents of the amplifier 54, as well as the resistances of theresistors R₁ and R₂, thus exhibiting a differential voltage V_(DIFF) atthe input of the amplifier 54. The differential voltage V_(DIFF) canthus be propagated in the output signals SGNL_(AMP) as noise, which, ifleft uninhibited, can cross the isolation barrier and reduce theperformance of the associated medical amplifier system.

By implementing isolation in the manner disclosed herein, the patientground 60 is caused to “float”, which is represented herein by the noisevoltage V_(NOISE) and a corresponding current I_(NOISE) that flows fromthe patient ground 60 to earth ground 70 via a parasitic capacitanceC_(P). The parasitic capacitance C_(P), for example, can result from acable coupling the patient circuitry stage 52 to the patient, a metalliccasing in which the patient circuitry stage 52 is housed, or a varietyof other ways. The parasitic capacitance C_(P) can be exhibited as asubstantially high-impedance current path to conduct a portion of thecurrent I_(NOISE) to flow as a current to earth ground 70.

To mitigate the effects of the noise voltage V_(NOISE), the system 50includes a shield around the patient circuits (connected to patientground) and capacitive coupling C_(GND) connected across the isolationbarrier 64 between the patient ground 60 to a functional ground 68. Thecapacitive coupling C_(GND) is configured with a capacitance that isgreater than the expected parasitic capacitance C_(P)(C_(GND)>C_(P)) asto provide a low-impedance current path between the patient ground 60and the functional ground 68 that resides in functional stage betweenthe respective isolation barriers 64 and 66. Therefore, the capacitivecoupling C_(GND) can conduct a much larger portion of the currentI_(NOISE) to flow as a current I_(GND) to functional ground 68. Thefunctional ground 68 is electrically isolated from earth ground 70 bythe one or more additional isolation barrier 66.

As a result of the inclusion of the capacitive coupling C_(GND) toconduct the current I_(GND) to earth ground 70, the effects of noise atthe input of the amplifier 54 based on induced currents I₁ and I₂ can besignificantly reduced. The substantially reduced noise at the input ofthe amplifier 54 can result in corresponding reduction in the noise thatis exhibited in signals SGNL_(AMP). For example, up to about 20 dBimprovement in common mode rejection ratio can be expected between aconventional circuit and a circuit employing a capacitive couplingC_(GND) coupled across the isolation barrier 64 between the patientground and functional ground 68. Accordingly, the associated medicalamplifier system 50 (e.g., the medical amplifier system 12) can maintainisolation of the patient from an associated power supply, includingearth ground 70, and can achieve superior performance with respect tomitigating noise in the signals SGNL_(AMP) that are received from thepatient and sent to across the isolation system to control andprocessing circuitry.

FIG. 3 depicts an example of an isolation system 100 such as can beimplemented in the medical amplifiers system demonstrated in examples ofFIGS. 1 and 2. The isolation system 100 is connected betweenpatient-side circuitry 102 and a non-isolated stage 104. In the exampleof FIG. 3, the patient-side circuitry 102 can include amplifiers,filters and the like, such as disclosed herein (e.g., FIG. 2).Additionally, as demonstrated in FIG. 3, the patient-side circuitry 102can include patient power circuitry 106 that is coupled to receive powervia the isolation system from an associated non-isolated power circuitry(e.g., a power supply) 114.

The patient power circuitry 106 can drive one or more voltage rails aswell as establish a patient ground 110. For example, the patient powercircuitry 106 can provide the voltage rail for supplying electricalpower to other patient-side circuitry including an analog-to-digitalconverter, demonstrated at 108. In this way, a digital version of thesensed input signal can be provided as the amplified signal SGNL_(AMP)that is supplied to a signal path of the isolation system 100. Theisolation system 100 thus can provide the corresponding digitized outputto the non-isolated stage including a non-isolated signal processingcircuitry 112. The signal processing circuitry 112 including filtering,digital signal processing and the like is designed to prepare themeasured signal. The signal processing circuitry 112 can further includepost-processing and visualization of the sensed signals, such as ECmapping or ECG and/or EEG diagnostics, which typically require a highsignal-to-noise ratio. The non-isolated power circuitry 114 can beconfigured to supply power to the non-isolating signal processingcircuitry directly and to the patient power circuitry across theisolation barrier as disclosed herein.

As disclosed herein, the isolation system 100 can include a plurality ofisolation barriers, demonstrated at 120 and 122. Intermediate therespective isolation barriers 120 and 122 can be a functional stage 124.It is to be understood that the medical amplifier system is not limitedto the two isolation barriers 120 and 122, but could include moreisolation stages than that disclosed herein. An additional advantage ofhaving two or more isolation stages is that each stage can be designedto withstand a proportional amount the required voltage as mandated by agiven medical device standard. For example, where two isolation stages120 and 122 are provided in a case where it is required to resist 4 KVAC, the components (e.g., transformers and optical isolators) of eachisolation stage can be designed to resist about 2 KV AC. Additionally,transformers are more efficient when isolating 2 KV than 4 KV.

The patient-side isolation barrier 120 can include multiple paths forproviding electrical isolation for both the signal path and electricalpower. For example, optical isolator circuitry can be connected betweenthe A/D converter 108 and the functional stage 124 for providing thesignal path through the isolation barrier 120. The optical isolationelement (e.g., including an optoisolator or optocoupler) can receivepower from the patient power circuitry, for example. The electricalisolation for the power path can be implemented via a transformer 128.

As disclosed herein, the isolation system 100 can include a capacitivecoupling C_(GND) connected between the patient ground associated withthe transformer 128 and a functional ground 129 that resides in thefunctional stage 124. The isolation stage 122 can be the same ordifferent from the isolation stage 120 such as including an opticalisolation element 130 for the signal path and a transformer 132 forproviding electrical isolation along the power path.

In the example of FIG. 3, the functional stage 124 can includeadditional circuitry and connections for completing the signal pathbetween optical isolation elements 126 and 130 as well as functionalpower circuitry, including connections 136, connected between thetransformers 128 and 132. As an example, the functional isolation stagecircuitry 134 can include additional filtering and/or amplifiersconfigured to perform additional pre-processing for the amplifiedsignals SGNL_(AMP). For example, digital filtering can be performed onthe digital signals provided from the optical isolation elements 126.Additionally, filtering and power conditioning can be implemented viathe functional power circuitry 136 for improving the power that isprovided to the patient power circuitry 106.

While each of the isolation stages 120 and 122 are disclosed asincluding optical isolation elements and transformers, the types ofisolation in the different stages can be the same (as shown) ordifferent. Additionally, different forms of isolation can be providedfor information-carrying signals and power from the optical andinductive isolation, such as may include capacitive, giantmagnetoresistive, electromagnetic waves, acoustic or mechanical means.

Furthermore, the medical amplifier system has been described as havingmulti-channel functionality, such that a plurality of patient signalsSGNL_(PTNT) and amplified signals SGNL_(AMP) can be communicated acrossmore than one signal channel in the isolation system. Such multichannelimplementations can include a single patient ground, a single functionalground and a single earth ground that is shared by the respectivechannels in each respective isolation stage in the system. As analternative example, the medical amplifier system could insteadimplement a separate medical amplifier system for each individualchannel, each having its own relative ground connections. Thus, themedical amplifier system can be configured in a variety of ways that candiffer from those disclosed herein.

What have been described above are examples. It is, of course, notpossible to describe every conceivable combination of components ormethodologies, but one of ordinary skill in the art will recognize thatmany further combinations and permutations are possible. Accordingly,the invention is intended to embrace all such alterations,modifications, and variations that fall within the scope of thisapplication, including the appended claims. As used herein, the term“includes” means includes but not limited to, the term “including” meansincluding but not limited to. The term “based on” means based at leastin part on. Additionally, where the disclosure or claims recite “a,”“an,” “a first,” or “another” element, or the equivalent thereof, itshould be interpreted to include one or more than one such element,neither requiring nor excluding two or more such elements.

What is claimed is:
 1. An apparatus comprising: an isolation systemconfigured to be connected between and provide electrical isolationbetween patient-side circuitry and non-isolated circuitry, the isolationsystem comprising: a patient isolation stage comprising at least onesignal input configured to connect to a signal path of the patient-sidecircuitry and a power input configured to connect to a power path of thepatient-side circuitry, at least one other stage connected between thepatient isolation stage and the non-isolated circuitry, the at least oneother stage comprising a corresponding signal path configured tocommunicate signals from the signal path of the patient-side circuitryto the non-isolated circuitry and a separate power path configured toprovide input power from the non-isolated circuitry to the power path ofthe patient isolation stage; a capacitive coupling connected across thepatient isolation stage between a patient ground of the patient-sidecircuitry and a functional ground of the isolation system, the at leastone other stage being configured to electrically isolate the functionalground from the non-isolated circuitry.
 2. The apparatus of claim 1,wherein the functional ground resides between the patient isolationstage and the at least one other stage of the isolation system.
 3. Theapparatus of claim 1, wherein the capacitive coupling is configured asone or more capacitors having a capacitance that is greater than aparasitic capacitance of the patient-side circuitry, whereby a lowimpedance path through the capacitive coupling to the functional groundis provided to reduce noise in the patient-side circuitry.
 4. Theapparatus of claim 3, wherein each of the patient isolation stage andthe at least one other stage is configured to provide one type ofelectrical isolation for the signal path thereof and another type ofelectrical isolation for the power path thereof extending between thepatient-side circuitry and the non-isolated circuitry.
 5. The apparatusof claim 1, wherein the at least one other stage is configured toelectrically isolate the functional ground from the non-isolatedcircuitry.
 6. The apparatus of claim 1, wherein the isolation systemfurther comprises a functional isolation stage comprising the functionalground and respective connections configured to pass the signals andpower between the patient-side circuitry and the non-isolated circuitry,the functional isolation stage being electrically isolated from thenon-isolated circuitry via the at least one other stage and beingisolated from the patient-side circuitry via the patient isolationstage.
 7. The apparatus of claim 6, wherein the functional isolationstage further comprises circuitry to process signals provided on thesignal path between the patient isolation stage and the at least oneother isolation stage.
 8. The apparatus of claim 1, wherein the signalpath of at least one of the patient isolation stage and the at least oneother stage comprises an optical isolation element for communicatingoptical signals through at least a portion for the isolation system. 9.The apparatus of claim 1, wherein the power path of at least one of thepatient isolation stage and the at least one other stage comprises atransformer to pass power through at least a portion of the isolationsystem.
 10. The apparatus of claim 9, wherein the transformer isconnected to the functional ground.
 11. A method of electricallyisolating patient-side circuitry from non-isolated circuitry in amedical amplifier, the method comprising: providing signals fromconductive elements on a patient to a patient isolation stage of themedical amplifier via the patient-side circuitry; providing input powerfrom the non-isolated circuitry to the patient isolation stage via apower path of at least one other stage connected between the patientisolation stage and the non-isolated circuitry; providing the signalsfrom the patient isolation stage to the non-isolated circuitry via theat least one other stage; electrically isolating a functional groundfrom the non-isolated circuitry via the at least one other stage andfrom the patient-side circuitry via a capacitive coupling connectedacross the patient isolation stage between a patient ground of thepatient circuitry and the functional ground.
 12. The method of claim 11,wherein the functional ground resides between the patient isolationstage and the at least one other stage.
 13. The method of claim 11,further comprising reducing noise in the patient-side circuitry byproviding a low impedance path through the capacitive coupling to thefunctional ground, the capacitive coupling being configured as one ormore capacitors having a capacitance that is greater than a parasiticcapacitance of the patient-side circuitry.
 14. The method of claim 13,further comprising providing different types of electrical isolation forthe signal path and the power path of each of the patient isolationstage and the at least one other stage extending between thepatient-side circuitry and the non-isolated circuitry.
 15. The method ofclaim 11, further comprising electrically isolating the functionalground from the non-isolated circuitry with an isolation barrier in theat least one other stage.
 16. The method of claim 11, wherein afunctional isolation stage comprising the functional ground andrespective connections is configured to pass the signals and powerbetween the patient-side circuitry and the non-isolated circuitry, thefunctional isolation stage being electrically isolated from thenon-isolated circuitry via the at least one other stage and beingisolated from the patient-side circuitry via the patient isolationstage.
 17. The method of claim 16, wherein the functional isolationstage further comprises circuitry to process signals provided on thesignal path between the patient isolation stage and the at least oneother stage.
 18. The method of claim 11, wherein the signal path of atleast one of the patient isolation stage and the at least one otherstage comprises an optical isolation element for communicating opticalsignals through at least a portion of the signal path.
 19. The method ofclaim 11, wherein the power path of at least one of the patientisolation stage and the at least one other stage comprises a transformerto pass power through at least a portion of the power path.
 20. Themethod of claim 19, wherein the transformer is connected to thefunctional ground.